The disclosed invention relates generally to head-up windshield hologram virtual image displays, and more particularly is directed to a head-up windshield virtual image display which produces a virtual image having image components located relatively far ahead of the windshield and in different virtual image planes.
Head-up displays for vehicles such as automobiles are utilized to produce a virtual image instrument display at or ahead of the vehicle windshield, which provides for increased safety since reading of the head-up display by the vehicle operator does not require shifting of the field of view or refocusing of the eyes.
Head-up displays generally produce virtual images by playback of an image hologram, which can be located on or in the windshield, or by reflection of an image source by a beamsplitter such as a coating applied to the windshield for example.
However, if a virtual image hologram system utilizes a broadband light source, the virtual image must be located close to the image hologram to avoid image blurring dispersion. In order to produce a virtual image relatively far ahead of the windshield that is not blurred, a narrowband light source must be utilized, which can be too expensive or too dim for some purposes.
With a head-up display in which the image originates in an image source it is difficult and probably not possible to produce multiple virtual images that are in different image planes and overlap with the more distant virtual images being viewable through the closer images.